$\begin{align}  & \frac{0.8\times 0.43\times 0.031}{0.05\times 0.72\times 0.021}=\frac{8\times {{10}^{-1}}\times 43\times {{10}^{-2}}\times 31\times {{10}^{-3}}}{5\times {{10}^{-2}}\times 72\times {{10}^{-2}}\times 21\times {{10}^{-3}}} \\ & \frac{0.8\times 0.43\times 0.031}{0.05\times 0.72\times 0.021}=\frac{8\times 43\times 31\times {{10}^{-1-2-3}}}{5\times 72\times 21\times {{10}^{-2-2-3}}} \\ & \approx \text{1}\text{.411}\times \frac{{{10}^{-6}}}{{{10}^{-7}}}\approx 1.411\times 10\approx 14.11\text{   }(4s.f) \\\end{align}$